Quasiparticle trapping by orbital effect in a hybrid superconducting-semiconducting circuit

Abstract

The tunneling of quasiparticles (QPs) across Josephson junctions (JJs) detrimentally affects the coherence of superconducting and charge-parity qubits, and is shown to occur more frequently in magnetic fields. Here we demonstrate the parity lifetime to survive in excess of 50 µs in magnetic fields up to 1 T, utilising a semiconducting nanowire transmon to detect QP tunneling in real time. We exploit gate-tunable QP filters and find magnetic-field-enhanced parity lifetimes, consistent with increased QP trapping by the ungated nanowire due to orbital effects. Our findings highlight the importance of QP trap engineering for building magnetic-field compatible hybrid superconducting circuits.

Singlet-doublet transitions of a quantum dot Josephson junction detected in a transmon circuit

“…For the transmon circuit the SQUID loop area is chosen to be small, ∼ 5 µm 2 , in order to suppress flux noise from misalignment in large parallel magnetic fields. Finally, InAs/Al nanowires, in which both junctions are defined, have been shown to support sizeable Josephson energies in fields in excess of 1 T [48,65]. Further details about device fabrication as well as the cryogenic and room temperature measurement setup can be found in the Supplementary Information (Section II) [60].…”

“…We now turn to time-resolved spectroscopy techniques to study the parity dynamics of the quantum dot junction close to the transition, aiming to characterize the lifetimes of singlet (even parity) and doublet (odd parity) states. These methods have previously been used to study quasiparticle dynamics in superconducting qubits [48,78], and recently also applied to a nanowire junction to study the poisoning of Andreev bound states [33,45,79].…”

“…To address this need, we have embedded a fully controllable quantum dot in a microwave superconducting circuit. This experimental choice is motivated by the success of circuit quantum electrodynamics (QED) techniques in the investigation of mesoscopic effects in Josephson junctions [32][33][34][42][43][44][45][46][47][48][49], which stems from its enhanced energy and time resolution compared to lowfrequency transport techniques. In this context, the microwave response of a quantum dot junction has attracted recent theoretical [50,51] and experimental [52] attention.…”

Parity switching in a full-shell superconductor-semiconductor nanowire qubit

“…The semiconductor platform offers advantages such as control of E J by electrostatic gating, and reduced charge dispersion without loss of anharmonicity [4,5]. The system has been developed to be compatible with large magnetic fields [6][7][8][9] where it potentially could be used for topological quantum computation [10,11]. With a magnetic field applied, NWs with a fully covering superconducting shell have been shown to exhibit destructive Little-Parks effect, both in dc transport and qubit measurements [12,13].…”

Dynamical polarization of the fermion parity in a nanowire Josephson junction

“…Theoretical proposals have investigated both sectors as qubit degrees of freedom [15][16][17][18], relying on conservation of parity. Although fermion parity is conserved in a closed system, superconducting circuits are known to contain a large non-equilibrium population of QPs [19][20][21][22][23][24][25][26][27][28][29][30]. These QPs can enter the junction and "poison" the ABS on timescales of ≈ 100 µs [10,31,32].…”